This week’s focus was entirely on getting the Vitis HLS build to work. We made really great progress with converting all the floating point numbers and operations to fixed point ones, stripping the code even further of unnecessary functions, and converting all the math operations from std to hls ones.
We’ve managed to get almost everything working, except for random number generation when making the particles. The goal for the rest of today and tomorrow is to get the Vitis HLS build completely working (which is a must for the interim demo) and have some way of sending the output from the FPGA code to the host computer, which can then render and evaluate the fluid against the baseline CPU version.
This week we got a lot of work done in terms of synthesizing the kernel. At the start of the week, we managed to get a synth running using floats as the main datatype. The problem with this one is that since floats were so computationally intensive, it was pretty much impossible to get the critical path to converge to the target critical path, and so we couldn’t meet timing. Nevertheless, this was a significant step in the right direction.
So my next task was to begin the migration from floats into our custom fixed point datatype. Basically any calculation we would perform on the particle positions or speeds, we would replace with a fixed point datatype. For now, we decided to use a fixed point representation where we have 6 bits representing the integral part of the number and 6 bits representing the fractional part of the number.
Unfortunately, this would prove to be quite an involved task, as we would also need to make significant changes to all of the math libraries in order to change them to use the new datatype. So, a majority of this week was spent incrementally compiling and changing the math libraries to use the arbitrary precision datatype instead of the floats. This was complicated by the fact that there were still some weird C++ issues that led to some weird aliasing of the datatype to the int datatype. Another specific issue we had to investigate was how we would take care of some specific math functions (such as square root); thankfully, this issue was easily addressed using the equivalents in the HLS math library. Other than that, we seem to have mostly figured out those issues, and now we have a compile running!
Build almost there! Still some kinks in our kernel to figure out
Our next step is to finalize the changes to get a complete synth of the kernel and then upload the project to normal Vitis so we can generate a binary file and upload it onto the board in time for the in-class demo. All in all, I am much more optimistic as to the effectiveness of our project after this week.
This week we did a lot of work on both some optimizations and synthesizability of our project. There were still many C++ errors from the interactions with the Vitis libraries and the modern C++ codebase that we are using. After initial synthesis attempts, it turned out the amount of floats, there was no way we could meet any sort of reasonable clock period for synthesis, so we began converting the code to use fixed point numbers as outlined in our design. But, the libraries provided by Vitis did not interact well with the already written math libraries, and I spent a while trying to get these libraries to cooperate with each other.
I think that we are on time, and are making steady progress towards the goals we set out to accomplish. We need to ensure that we work consistently in the upcoming weeks, but we have been working well recently. Next week I hope to work more on optimizations with unrolling and pipelining.
In my last update, the main goal I wanted to tackle was getting the evaluation script to work with the fluid simulation output. Unfortunately, I was not able to accomplish this as all of my time for this week was spent on working with Ziyi and Jeremy to get the Vitis HLS build working.
We’ve been in the lab nearly every day, and thankfully we are really close to being done. We just have some issues with random number generation for the initial positions of the particles, and dealing with some last minute replacements of std math functions with hls functions.
The demo is Monday, and while we are in an OK spot I am still a bit worried about it. I’m staying up all night today to aim to get it working by tonight in case we run into new issues tomorrow.
